If someone has the right to ‘buy back’ the foreclosed property (in CA), and the property has already had all the back property taxes paid up and remodeling started/finished. Do they still only have to pay the amount that the property was sold for at Auction? What about all the expenses put into the property after the foreclosure and eviction?

Miketh is right. The trustee who authorized the property sale, a court, and the IRS are just about the only entities who can have something to say (i.e. intervene, overturn or in the case of the IRS redeem w/in 120 days) post trustee sale.

Perhaps you’re thinking about those rare occasions when (prior to the issuance of the trustee’s deed upon sale - TDUS), a trustee opts to rescind a trustee sale? The most common reason for a “rescission” is a when a foreclosed upon homeowner filed a BK before the trustee sale and properly notified the trustee … In other words, the trustee erred by going forward with the sale and is now trying to remedy the situation by rescinding the sale … Again, this rescission can happen, but in most cases BEFORE the TDUS has been issued. That is one good reason why a trustee sale buyer should defer any major rehab/fix-up expenses on their newly acquired property until AFTER they have received and recorded the TDUS (about 5 to 10 days post auction on average). It is much more difficult for any party (IRS redemption excepted) to overturn a sale AFTER the TDUS has been issued, and the new buyer most likely would have to be compensated for any expenses they’ve incurred to fix-up/rehab the property.